This invention relates to an X-ray image correction apparatus and, in particular, to an X-ray image correction apparatus which is used in an X-ray diagnosis system in which an X-ray contrast medium is injected into the patient for performing X-ray diagnosis.
Recently, attention has been drawn to systems in which the video signal from an X-ray television camera, which uses an X-ray image intensifier, is processed to obtain an X-ray diagnosis image of the patient. However, if the video signals of the camera are displayed as is on the screen, unwanted images will also be included in the image, making diagnosis difficult. A method has been developed in which the unwanted images are eliminated and only those images required for diagnoses are displayed. This is called the subtraction method. In this method, images obtained before and after the patient is injected with an X-ray contrast medium are subtracted to cancel out the unwanted images. For example, in a cerebral angiograph image, the image of the cranium before the contrast medium is injected (mask image) and the superposed image of the cranium image and the blood vessel image after the medium has been injected are subtracted to cancel out the cranium image, leaving behind a blood vessel image of high contrast.
With this subtraction method based on the injection of contrast medium into the vein, the X-ray contrast medium injected into the patient flows from the veins to the heart to the arteries. After the first X-ray image of the desired location is taken, the medium is injected and, after a specified time calculated based on the speed of the medium has elapsed for the medium to reach the desired location, a second X-ray image is taken. If the patient moves during this time gap between the first and second images, the location to be diagnosed is moved and the image obtained by subtraction processing of the first and second image will contain undesired images, resulting in a reduction in image quality.